In the past, ignition of mixture in an internal-combustion engine such as a reciprocating engine and a rotary engine was carried out by an ignition plug for performing spark discharge. However, there has been suggested an ignition apparatus that performs ignition using electromagnetic wave with frequency of several gigahertzes (GHz), that is microwave irrespective of the spark discharge, since electromagnetic noise that occurs by the spark discharge causes erroneous operation of an electronic device mounted on a vehicle.
For example, the ignition apparatuses in which a microwaveguide is configured to be connected to a combustion/reaction chamber (in a cylinder) and a discharge electrode for making microwave discharge is provided in the combustion/reaction chamber is disclosed in Patent Documents 1 to 4.
In the ignition apparatus, microwave pulses generated by a microwave generation unit (magnetron) are transmitted through the microwaveguide to the inside of the combustion/reaction chamber and microwave corona discharge is caused by the discharge electrode to ignite mixture in the combustion/reaction chamber.
For example, according to Patent Document 5, there is disclosed a gasoline internal-combustion engine in which a high frequency electric field generator (magnetron) is provided in the combustion/reaction chamber (in a cylinder) so that the high frequency electric field generator forms a high frequency electric field in the combustion chamber during the step of a compression stroke of the engine to perform dielectric heat, ignite, and burn mixture in the combustion chamber.
In the conventional plasma equipments used in the environmental countermeasure technologies, in general, high-temperature thermal equilibrium plasma is generated by increasing energy input into plasma generated by making discharge under low pressure to heat hazardous effluents, chemical substances, suspended particulate matters, soot and the like to high temperature so as to oxidize and degrade them.
Recently, a method (coaxial resonator-type plasma generation) of generating atmospheric thermal non-equilibrium plasma by microwave discharge has been studied. The generated plasma is reactive plasma in which temperature of electron is tens of thousands and temperature of gas is in the range of normal temperature to 1,000° C. In addition, a plasma equipment for a sterilization/disinfecting/odor elimination used in a medical/hygiene field has been developed by using effect of strong chemical reaction of OH radical, O3 (ozone), and the like generated by the plasma (Innovation Japan 2005; http://ccr.ccr.tokushima-u.ac.jp/topic/050927-01.pdf).
A plasma equipment using the microwave allows gas with the pressure close to the atmospheric pressure to be excited by the microwave so as to generate plasma gas.
For example, a microwave plasma equipment is disclosed in Patent Documents 6 and 7. In the microwave plasma equipment, a non-metal pipe for a gas flow channel is disposed along the center of a central conductor, and gases injected from one end are excited by the microwave at a gap where the non-metal pipe is not covered with the central conductor, and then are induced plasma (coaxial resonator-type plasma generation) and discharged from the other end.    [Patent Document 1] JP-A-57-186067    [Patent Document 2] JP-A-3-31579    [Patent Document 3] JP-A-2000-230426    [Patent Document 4] JP-A-2001-73920    [Patent Document 5] JP-A-2000-274249    [Patent Document 6] JP-A-2001-035692    [Patent Document 7] JP-A-2004-172044